CAPE CANAVERAL, Fla. - Thursday marks 35 years since the space shuttle Challenger disaster. It is also NASA's annual day of remembrance to honor the astronauts who have lost their lives during missions.Hundreds of people in Florida and millions watching on live television witnessed the space shuttle Challenger break apart in a mid-air explosion on January 28, 1986, killing 7 people on board.The blast occurred 73 seconds after takeoff from the Kennedy Space Center in Cape Canaveral, Fla.